Possible discrepancy on notation

[040902fyn]

On page 11 of the book, the definition of trajectory shows that the action taken on state $s_t$ is $a_t$

However, on ppt (which is in the lecture on bilibili) shows the action taken on state $s_t$ is $a_{t + 1}$

Seems to have some discrepancy on notation. Which notation should I follow?

[MathFoundationRL]

When you see discrepancy, please follow the latest version of the book. Some minor issues in the video cannot be updated once recorded.

[040902fyn]

Understood. Thanks!